Re: Tracking last scan time

[Michael Paquier]

On Thu, Nov 03, 2022 at 04:44:16PM -0400, Dave Page wrote:
> Here's a patch to fix this issue. Many thanks to Peter Eisentraut who
> figured it out in a few minutes after I spent far too long looking down
> rabbit holes in entirely the wrong place.

FWIW, all the other areas of pgstatfuncs.c manipulate timestamptz
fields with a style like the attached.  That's a nit, still per the
role of consistency with the surroundings..

Anyway, it seems to me that a regression test is in order before a
scan happens just after the relation creation, and the same problem
shows up with last_idx_scan.
--
Michael

diff --git a/src/backend/utils/adt/pgstatfuncs.c 
b/src/backend/utils/adt/pgstatfuncs.c
index 96bffc0f2a..ae3365d917 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -56,12 +56,18 @@ Datum
 pg_stat_get_lastscan(PG_FUNCTION_ARGS)
 {
        Oid                     relid = PG_GETARG_OID(0);
+       TimestampTz result;
        PgStat_StatTabEntry *tabentry;
 
        if ((tabentry = pgstat_fetch_stat_tabentry(relid)) == NULL)
+               result = 0;
+       else
+               result = tabentry->lastscan;
+
+       if (result == 0)
                PG_RETURN_NULL();
        else
-               PG_RETURN_TIMESTAMPTZ(tabentry->lastscan);
+               PG_RETURN_TIMESTAMPTZ(result);
 }
 
 
diff --git a/src/test/regress/expected/stats.out 
b/src/test/regress/expected/stats.out
index 257a6a9da9..1d84407a03 100644
--- a/src/test/regress/expected/stats.out
+++ b/src/test/regress/expected/stats.out
@@ -573,6 +573,12 @@ SELECT pg_stat_force_next_flush();
  
 (1 row)
 
+SELECT last_seq_scan, last_idx_scan FROM pg_stat_all_tables WHERE relid = 
'test_last_scan'::regclass;
+ last_seq_scan | last_idx_scan 
+---------------+---------------
+               | 
+(1 row)
+
 COMMIT;
 SELECT pg_stat_reset_single_table_counters('test_last_scan'::regclass);
  pg_stat_reset_single_table_counters 
diff --git a/src/test/regress/sql/stats.sql b/src/test/regress/sql/stats.sql
index f6270f7bad..b4d6753c71 100644
--- a/src/test/regress/sql/stats.sql
+++ b/src/test/regress/sql/stats.sql
@@ -303,6 +303,7 @@ BEGIN;
 CREATE TEMPORARY TABLE test_last_scan(idx_col int primary key, noidx_col int);
 INSERT INTO test_last_scan(idx_col, noidx_col) VALUES(1, 1);
 SELECT pg_stat_force_next_flush();
+SELECT last_seq_scan, last_idx_scan FROM pg_stat_all_tables WHERE relid = 
'test_last_scan'::regclass;
 COMMIT;
 
 SELECT pg_stat_reset_single_table_counters('test_last_scan'::regclass);

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